Removal of weak acids and ammonia from gases



' June 30, 1936. H. BIAEHR y REMOVAL OF WEAK ACIDS AMD AMMONIA FROM GASES Filed June so, 1953 Patented June 30, 1936 PATENT gOFFICE REMOVAL F WEAK ACIDS AND AMMIONIA FROM GASES Hans Bae'hn Leuna, Germany, assigner to- I. G.

Farbenindustrie Aktiengesellschaft, Frankforton-the-Main, Germany Application June so, issaseai No. 618,357 In Germany July 5,1932

The present invention relates to the removalof weak acidsyand ammonia from gases, more particularly with the recovery oi ammonium sulphite or ammonium thiosulphate or of ammonium sulphate and sulphur.

It has already been proposed to remove hydrogen sulphide and ammonia from gases by absorption with ammonium sulphite-bisulphite liquors or ammonium polythionate liquors, the exhausted scrubbing solutions being worked up into ammonium sulphate and sulphur by treatment with sulphur dioxide and boiling. When employing this method it is important that the proportions of ammonia and hydrogen sulphide in the crude gas are the same in which the two gas constituents occur in the iinal products. If a corresponding adjustment oi the proportions of the two gas constituents is not maintained, the excess of the one constituent remains in the gas; this necessitates an expensive afterpurication. A further drawback of the said process consists in the fact that the cyanogen compounds react with the polythionate compounds with the formation of ammonium thiocyanate which can onlyV be difiicultly removed from the ammonium sulphate liquors, so that the resulting salt is liable to have a red color by the formation of iron thiocyanate. Furthermore, 'by the said process it is -generally speaking impossible to remove carbon dioxide.

I havenow found that the said drawbacks are "obviated by removing the weakly acid constituents, such as carbon dioxide, hydrogen sulphide and cyanogen compounds from the gas by means of 'a' scrubbing process in which the weakly acid constituents are recovered from the scrubbing medium assuch, the hydrogen sulphide, recovered by expelling it from the scrubbing liquid, then being brought into reaction in a. suitable manner with the ammonia.

The gases are accordingly rst scrubbed with q a scrubbing liquid so that the weakly acid constituents are absorbed, the hydrogen vsulphide which escapes (together with carbon dioxide and 4'5 hydrocyanic acid) when theenriched scrubbing liquid is heated is then burned to form sulphur dioxide and the latter employed for reaction with ammonia, ammonium sulphite. or ammonium thiosulphate in the manner already known i'or 50 the so-called polythionate process. For the purpose of scrubbing out hydrogen sulphide. anyl scrubbing liquid which absorbs hydrogen sulphide at ordinary temperature and yields it'up again at elevated temperature may be employed. 5 scrubbing liquids which have this action are f or.

Upolythionate liquors in the usual manner.

example amines or aqueous solutions oi.' amines, especially hydroxyalkylamines such as triethanol amine, diethanol amine and butanol amine, alkali metal and alkali earth metal salts of amino acids, as for example of glycocoll, alanine, or al- 5 kaline solutions of phenols, or also solutions of alkylol amines or alkyl-alkylol-amines in hydrocarbon liquids such as tar oils, parailin oils and the like. 'I'he absorption of the hydrogen sulphide may take place in the presence of the am- '10 monia or after previous absorption of the same by means of faintly acid ammonium sulphite or polythionate solutions. The hydrogen sulphide absorbed by the scrubbing liquid is expelled therefrom by heating and burned with air or oxygen. 15

\ 'I'he resulting sulphur dioxide then serves for the conversion of ammonium sulphite liquors into ammonium sulphite-bisulphite liquors or of ammonium thiosulphate liquors into ammonium ammonium, sulphite-bisulphite or ammonium polythionate liquors thus obtained are then used for scrubbing out the ammonia from the gas either before or after the removal of the weakly acid constituents. When the removal oi' the am- 25. monia is `effected after the scrubbing out of the hydrogen sulphide, any small amounts ofl hydrogen sulphide not vabsorbed by the scrubbing liquor and still present in the gas are also absorbedby this treatment so that simultaneously a flnal puri- 30 fication of the gas is' attained.

Y, In order to work up the liquors containing ammonium sulphite or ammonium thiosulphate obtained by purifying the gases from ammonia into ammonium sulphate and sulphur, the ammonium 35 sulphite is boiled with sulphur or substances which split off sulphur and thus converted into ammonium thiosulphate, the latter is treated with sulphur dioxide (which may likewise be obtained by burning hydrogen sulphide) and thus con- 40 verted into ammoniumpolythionate which when heated decomposes to form ammonium sulphate and sulphur.

By reason ci' the fact that the absorption oi' the hydrogen sulphide is eiected by a special scrubbing process, the proportion of ammonia simultaneously present in the gas has -no eiect on the degree of purification of the gas, contrasted with the usual polythionate process. The process according to the present invention therefore has the great advantage over all processes hitherto known that the ratio of amionia to hydrogen sulphide in the gas plays no part in the' purification thereof so that gases having the most varied contents of ammonia and hydrogen sulphide may The 20' be directly employed. ployed in which, besides Gases may even be emhydrogen sulphide, there Abing tower monia derived from other sources may be employed. If, on the other hand, in addition to hydrogen sulphide there is an excess of ammonia present in the gas, the excess of ammonia may be removed by absorption in acids or water. Similarly any deficiency of sulphur dioxide may be made good by burning sulph The following examples, given with reference to the accompanying drawing which diagrammatically illustrates arrangements of apparatus suitable for carrying out the process according to this invention, will further illustrate the nature of rthe invention, but the invention is restricted neither to these examples nor to the arrangements shown in the drawing. In Figure 2 of the drawing, parts corresponding to those indicated in Figure 1 areindicated by the same referen numbers.

Example 1 Referring to Figure 1, coke oven gas containing 8 grams of ammonia, 12 grams of hydrogen sulphide, 1.2 grams of cyanogen and cyanogen compounds and35 grams of carbon dioxide per cubic meter is trickled, after cooling to about 25 C., in a scrubbing tower I with an acid ammonium polythionate liquor leading in of sulphur dioxide the ammonia thus being wholly absorbed while the hydrogen sulphide is only absorbed to a slight extent. 'Ihe 'gas is then trickled .with a 50 per cent aqueoustriethanol amine solution in a scrubbing tower 2, the hydrogen sulphide and the cyanogen compounds being thus wholly, and the carbon dioxide partly, removed from the gas. T'he vexhausted triethanol amine solution collects in a container 3 and is preheated to about 80 C. in a heat. exchanger l by hot regenerated liquor; the carbon dioxide, hydrogen sulphide and cyanogen are expelled from the gas by blowing steam into a column 5. The hot triethanol amine solution gives up its heat to the used solution in the heat exchanger 4 and then passes back into the scrubbing tower V2. The'hydrogen sulphide expelled is burned with-air in a furnace-.6 and the resulting sulphur dioxide, after cooling in a cooler 1 is absorbed by 4ammonium thiosulphate solution in an absorption tower 8.

The coke oven gas, after its treatment with 'the triethanol amine-solution in the scrubbing tower 2, still contains small amountsl of hydrogen sulphide and in order to'eifect the iinalpuriiication is triokled in a scrubbing tower 9 with the faintly ammoniacal. ammonium thiosulphateammonium polythionate solution flowing from thionate solution absorbs the residual amount of hydrogen sulphide with the formation lof ammonium thiosulphate; the solution collects in a container I0 from whi..n it is pumped into an absorption tower 8v for regeneration with sulphur dioxide. The regenerated ammonium thiosulphate solution is in part pumped into the scrub- I for scrubbing out ammonia and the excess is boiled in the usual manner to form ammonium sulphate and sulphur.

Solutions of the polythionates of alkali or heavy metals may be used instead of the ammonium polythionate solution.

Examplez Referring to Figure 2, cokey oven gas having freshly regenerated by the The ammonium poly- `ammonium sulphite containing small amounts of ammonium bisulphite. v The ammonia is thusremoved fairly completely from the gas. The gas is then scrubbed in a scrubber 2 with an approximately 30 per cent solution of sodium alanine, the

' hydrogen sulphide and the cyanogen compounds being thus almost completely', and the carbon dioxide about half, absorbed by the washing liquid. The used sodium alanine solution is forced from the collecting container l3 through a heat exchanger l into a steam heater from which it then passes into a column apparatus V5 arranged below said steam heater. The steam expels the acid constituents from the scrubbing liquor trickling down in counter-current through vthe single partitions of the column. The purified solution passes through the heat exchanger l and then to the top of the scrubber 2. The hydrogen sulphide is burned in a furnace 8 to form sulphur dioxide which is absorbed in an absorption tower 8 by the ammonium sulphite solution coming from the preliminary scrubber I with the formation of an ammonium sulphiteammonium bisulphite solution. This latter solution collects in a. container II and is forced to a scrubbing tower I2 for the final purification of the gas. In the said scrubbing tower I2, the residual amounts of hydrogen sulphide and ammonia are removed from' the gas so that the gas leaving the said scrubbing tower is completely purified.

A part of theV ammonium sulphite solution which is not `required for the final purification of the gas in the scrubbing tower I2 is converted by boiling with sulphur into ammonium thiosulphate and converted into ammonium polythionate by leading in sulphur dioxide. By boiling the ammonium polythionate solution, ammonium sulphate and sulphur are formed. According to the specified composition of the gas with 8 grams of ammonia and 12 grams of hydrogen y same,'which comprises scrubbing said gas with an aqueous solution of ammonium polythionate, thereby removing ammonia from gas, passing the resulting gas into contact with a substance capable of absorbing hydrogen which hydrogen sulfide can be recovered as such, thereby removing the majorportion of the hydrogen sulfide, contacting the resulting gas with the solution of ammonia resulting from the first scrubbing in order to remove hydrogen sulfide therefrom, leaving a pure gas, recovering the hydrogen sulfide from the solution of hydrogen suliide resulting from the second scrubbing, burning the, hydrogen sulfide to sulsulfide and from o0 the last traces of 65 fur dioxide, reactingthe sulfur dioxide so formed 70 with the solution obtained from the third scrubbing step to regenerate the same, and-recycling said regenerated polythionate solution to the first scrubbing step.

` HANS BAEHR. 

